Thousands of protesters gathered yesterday on the southern Japanese island of Okinawa to rally against plans to relocate a US air base there, with reports saying the protesters numbered as many as 35,000.

Despite pressure to move the Futenma Air Base off Okinawa, Japan and the United States agreed last October on a revised plan to transfer the facilities to an existing base at Camp Schwab, also on the island.

Holding placards demanding the immediate closure of the base and its relocation off the island, about 35,000 people took part in the rally in Ginowan, Kyodo News and public broadcaster NHK reported.

"The city of Ginowan strongly demands that Futemma, the world's most dangerous base, be shut down immediately and relocated outside of Japan," Ginowan Mayor Yoichi Iha was quoted as saying in the Kyodo report.

Tokyo and Washington have held marathon talks since 1996 on relocating Futenma Air Base out of the crowded urban centre of Ginowan, where residents complain about aircraft noise.

Residents' opposition against the US military presence was heightened in August last year, when a Marine helicopter crashed on a college building in Ginowan and fell on its campus. No one was injured.

"If there is no US bases in Okinawa, it will be good and safe for our children," a local woman participating in the rally told NHK.

But few other communities are willing to host US bases, which are in the country under a security alliance as Japan has been officially barred from keeping a military since World War II.

The United States had initially planned to move the base to reclaimed land on the sea off a quiet fishing village within Okinawa but that proposal led to opposition by residents and environmentalists.

A bilateral deal reached last October in Washington agreed to transfer Futenma's facilities to Camp Schwab and to withdraw 7,000 Marines from the tiny province.

Later Washington agreed to up the number of Marines being withdrawn to 8,000.

Iwakuni, another southwestern city, will vote next Sunday on whether to allow more US warplanes on its soil, in a largely symbolic referendum on the controversial plan to shift US forces in the country.

The outcome of the March 12 referendum, a rare exercise in Japanese direct democracy, is not binding. But it could affect efforts by Tokyo and Washington to finalise a sweeping plan to reorganise the 50,000 US troops in Japan, part of Washington's effort to transform its military into a more flexible force.

Part of the plan calls for the transfer of 57 carrier-based planes and about 1,600 military personnel from Atsugi Naval base near Tokyo where locals have long complained of flight noise to Iwakuni, about 1,000 kilometres west of the capital and already home to more than 3,000 Marines and 57 US aircraft.

The transfer would take place in 2009 after completion of an offshore runway built on reclaimed land.

In return, 17 Japanese planes and 700 Japanese military personnel would move to Atsugi.

"Flight noise is the biggest worry," said Miyano, 26, one of about 100 people who gathered at a public hall late last week to hear Iwakuni Mayor Katsusuke Ihara explain the referendum.